At some point in our lives we’ve heard that we should drink around six to eight glasses of water a day. It’s a recommendation that’s rarely challenged and championed by many health advocates. But where exactly do the numbers come from and why? Dr. Margaret McCartney, a general practitioner from Scotland, is challenging the 8-glasses-a-day rule and recently published her thoughts in an article entitled “Waterlogged?” in the British Medical Journal.

Dr. McCartney describes the notion that “we don’t drink enough water” as “thoroughly debunked nonsense,” and that having too much water could be unhealthy. She notes that the recommendation to drink six to eight glasses of water a day is supported by many health officials and organizations, including the NHS (National Health Service). The NHS Choices website even states on its website that we should “try to drink about six to eight glasses of water (or other fluids) a day to prevent dehydration. When the weather is warm or when we get active, we may need more.”

McCartney’s claim is bold, no doubt, but she cites two major sources as evidence. First, Heinz Valtin wrote in the American Journal of Physiology in 2002 that that there is “no scientific evidence that we need to drink that much [water]” and that the “recommendation could be harmful.” Also, a 2008 editiorial in the Journal of the American Society of Nephrology stated that “there is no clear evidence of benefit from drinking increased amounts of water…there is simply a lack of evidence in general.”

Others are rushing to support Dr. McCartney’s assertions and are relieved that she’s contributing to this ongoing conversation. The Guardian notes that “we humans are pretty good at regulating our own water intake. When we need to replace fluid there’s this highly accurate mechanism called thirst that prompts us to have a drink.”